Motorized drain cleaners incorporating a rotating cable, commonly referred to as a snake, have been used for many years. Some types of drain cleaners use a Permanent Split Capacitor (PSC) AC electric motor for motive power. However, the output torque for a PSC/AC motor may fall off rapidly as the motor speed decreases under load, as illustrated in Graph A. Further the PSC/AC motor may overheat under light loads, thereby requiring an external cooling fan to keep it cool. This inherent characteristic of the PSC/AC motor may make the PSC/AC motor undesirable for use on rotary drain cleaners. As the rotary cable, or snake, meets a stubborn obstacle the rotating cable may slow down thereby resulting in an undesirable torque decrease and the possibility of motor overheating. Due to an inadequate level of performance, the PSC/AC motor may not be suitable for operation at variable speeds or applications requiring the motor to produce rotation at variable speeds.
One alternate type of motorized, rotating cable drain cleaner described in U.S. Pat. No. 4,763,374 issued to Kaye, Aug. 16, 1988, disclosed a motorized drain cleaner that included a permanent magnet motor. In a preferred embodiment, the cleaner incorporated a 12-volt DC motor. However, Kaye only disclosed a cleaner comprising a trigger switch to toggle the motor between on and off settings. The device described in Kaye fails to provide a user the ability to vary the operating speed of the motor during operation, which may hinder the user's ability to effectively and safely remove obstructions from a sewer or drain.
While numerous motorized drain cleaners have been made and used for removing obstacles in drains and sewers, it is believed that no one prior to the inventors has made or used the invention described in the appended claims.